1. Field of the Invention
The present invention relates to an integrated power device having a start-up structure. More specifically the invention relates to the integration of a start-up structure in a power device.
2. Discussion of the Related Art
The invention relates, in particular, but not exclusively, to a multi-drain (MDmesh) MOSFET power device, and the ensuing description is made with reference to this field but only for the purpose of simplifying the explanation.
In the course of the last few years, particular interest has been directed to semiconductor power devices for switched-mode power-supply (SMPS) applications, which include control circuits. Power devices in which control functions are integrated, which enable, for example, self-protection of the power device in all operating conditions, are referred to as SMART-Power devices. For these devices, studies have been conducted on the integration also of the start-up part, for the purpose of increasing the efficiency of the power devices. In fact, the integration of the start-up function in the SMPS application enables a reduction in the dissipation of the devices in stand-by conditions, a reduction in the start-up times and a reduction in the number of external components.
According to the prior art, in smart power devices, the start-up function is currently integrated by inserting, within the IC control device, a high-voltage device, for example a MOSFET made up of just a few cells. However, in the majority of cases, this entails substantial problems in the fabrication of the IC control device. For example, integration of the IC device, which must be a high-voltage one, entails high production costs, in so far as it must be obtained on a high-voltage epitaxial thickness capable of supporting the inhibition voltage required and enable introduction of the necessary edge structure.
In addition, the fabrication of the IC control device on a high-voltage epitaxial thickness causes problems linked to the production of the IC device. In fact, when this is inhibited, if a voltage is applied from the outside which is higher than the breakdown voltage of the IC device, a process of avalanche multiplication is triggered therein and produces a current (avalanche current) that can destroy the IC device. If the inhibition voltage of the IC device is higher than the inhibition voltage of the MOSFET power device, the avalanche current will traverse the MOSFET power device, preventing problems to the IC device. Consequently, its inhibition voltage must be always higher than that of the MOSFET power device. On the other hand, the variability of the production process in the fabrication of the MOSFET power device and of the IC device requires that the inhibition voltage of the IC device should be much higher than that of the MOSFET power device. When this does not occur, there is destruction of the entire SMART-Power device.
Consequently, it is of particular importance to identify new and readily implementable strategies of integration of the start-up function, for the purpose of increasing the efficiency of the device and eliminating the risk of destruction of the SMART-Power device on account of the variability of the process.